The sulfur additive in powder catalysts affects synthetic diamonds in the following detailed ways:
Changes in Catalyst Characteristics and Impact on Growth Process Sulfur, as a trace element additive, is incorporated into powder catalysts (such as Fe-Ni catalysts). This additive can significantly alter the characteristics of the catalyst, thereby influencing its catalytic action to a certain extent. This, in turn, changes the growth conditions, mechanism, and process of diamond, ultimately affecting various properties of the diamond, including its morphology, color, strength, and internal inclusion distribution.
Impact on Diamond Morphology
Overall Crystal Shape: When synthesized using Fe-Ni catalysts with sulfur additive in a domestic cubic anvil high-pressure apparatus, most diamond crystals are cubo-octahedral and possess a complete crystal shape.
Appearance of Etch Pits on Faces: This is one of the most significant morphological features of diamonds synthesized with sulfur-containing catalysts. Etch pits typically appear on the faces of most diamond crystals synthesized with sulfur-added Fe-Ni catalysts, a phenomenon absent in diamonds synthesized without the sulfur additive. Both optical microscopy and electron microscopy observations confirm this. These etch pits usually manifest as many irregular indentations aggregated in a specific area.
Integrity of Faces: In contrast, the faces of diamond crystals containing the sulfur additive are relatively complete.
impact on Diamond Growth Mechanism
Disruption of Crystal Lattice Arrangement: The appearance of etch pits indicates that the addition of sulfur elements disrupts the lattice arrangement of the {100} crystal faces during diamond growth.
Selective Adsorption Effect: Research speculates that this disruption and the etch pit phenomenon are caused by the selective adsorption of sulfur or sulfides on the faces of the diamond. The influence of impurities on crystal growth morphology is often due to the selective adsorption of impurities on crystal faces, and this adsorption alters the relative growth rates of the crystal faces, thereby contributing to changes in crystal morphology.
Impact on Diamond Internal Structure and Properties
Significantly Reduced Inclusion Content: The inclusion content in diamond crystals synthesized with sulfur-added Fe-Ni catalysts is remarkably lower than that in diamonds synthesized without the sulfur additive.
Inhibition of Inclusion Entry: Optical microscopy observations reveal that this phenomenon suggests that the addition of an appropriate amount of sulfur plays a certain inhibitory role in the entry of inclusions during diamond growth.
Diamond Color Change: Due to the difference in internal inclusion content, diamonds synthesized with sulfur-added catalysts appear light yellow, while those synthesized without the sulfur additive exhibit a dark yellow color.
Control of Inclusion Distribution: Overall, adding an appropriate amount of sulfur to the mixed system of Fe-Ni catalyst and graphite helps control the content of inclusions in diamond.